In July 1819 a contemporary from Britain visited Luxembourg: his journal offers some insights. Norwich Duff, writes of its city that "Luxembourg is considered one of the strongest fortifications in Europe, and … it appears so. It is situated in Holland (then as now used by English speakers as shorthand for the Netherlands) but by treaty is garrisoned by Prussians and 5,000 of their troops occupy it under a Prince of Hesse. The civil government is under the Dutch and the duties collected by them. The town is not very large but the streets are broader than [in] the French towns and clean and the houses are good.... [I] got the cheapest of hot baths here at the principal house I ever had in my life: one franc."
Much of the Luxembourgish population joined the Belgian revolution against Dutch rule. Except for the fortress and its immediate vicinity Luxembourg was considered a province of the new Belgian state from 1830 to 1839. By the Treaty of London in 1839 the status of the grand duchy was confirmed as sovereign and in personal union to the king of the Netherlands. In turn, the predominantly French speaking part of the duchy was ceded to Belgium as the province de Luxembourg.
This loss left the Grand Duchy of Luxembourg a predominantly German state, although French cultural influence remained strong. The loss of Belgian markets also caused painful economic problems for the state. Recognizing this, the grand duke integrated it into the German Zollverein in 1842. Nevertheless, Luxembourg remained an underdeveloped agrarian country for most of the century. As a result of this about one in five of the inhabitants emigrated to the United States between 1841 and 1891.